1. Field of the Invention
The present invention relates to a thyroid radiation uptake measurement apparatus, and more particularly to a thyroid radiation uptake measurement apparatus for measuring an uptake extent of a radioisotope adsorbed in a thyroid to determine if the thyroid is functionally abnormal.
2. Description of the Prior Art
As generally known in the art, a thyroid is an endocrine organ secreting a thyroid hormone controlling a body's metabolism, which is positioned in front of a thyroid cartilage. Thyroid diseases include thyrotoxicosis, hypothyroidism, thyroiditis, thyroid nodule, thyroid cancer, and the like.
From among various apparatuses used for diagnosing a thyroid disease, a thyroid uptake measurement apparatus is especially an apparatus using nuclear medicine, in which the adsorption/uptake extent of an orally administered (or intravenously injected) radioisotope, such as, iodine (123I or 131I) or 99μTc (Technetium), on a thyroid is measured to determine if the thyroid is abnormal.
A radiation detector which is a main component of a conventional thyroid uptake measurement apparatus generally includes a photomultiplier, a scintillator, and a collimator.
In the operation process of the above mentioned conventional thyroid uptake measurement apparatus, when gamma rays emitted from radiation adsorbed in a thyroid react to the scintillator via the collimator, the incident gamma rays are converted into light, and the light is converted into electrical signals via the photomultiplier. Herein, a high voltage of up to several thousand volts (V) is applied so that the photomultiplier can carry out amplification through conversion of the light into electrons. For this reason, a separate high-voltage generating device is required. Also, the electrical signals generated from the photomultiplier are amplified via an amplifier circuit, and the amplified signals are processed to be used for obtaining quantitative information of radiation.
A protocol for such a thyroid test is differently carried out depending on the kind of radiation used and the object of test. However, a basic procedure is based on the method suggested by Society of Nuclear Medicine (SNM). The kinds of radioisotopes used and the levels of injected drugs are noted in “Radiation dosimetry for adults” in Table 1.
TABLE 1Organ receivingAdministeredthe largestEffective doseRadiopharma-activityradiation doseequivalentceuticalMBq(mCi)mGy/MBq(rad/mCi)mSv/MBq(rem/mCi)NaI-1233.7-11.1po3.2 Thyroid(12.0)0.11 (0.41)iodide*(0.1-0.3)99mTc-0.062 ULI**pertechnetate74-370 (2-10)(0.23) 0.013 (0.048)(TcO4−)Na1-31I0.15-0.37po360 Thyroidiodide(0.004-0.01)(1300)  11 (41.0)*assuming 25% uptake**ULI—upper large intestineReferences:1. Micheal F. Stabin, PhD, CHP: Radiation Internal Dose Information Center, Oak Ridge Institute for Sience and Education, Oak Ridge, TN, 1996.2. ICRP Publication 53, Radiation Dose to Patients from Radiopharmaceuticals, 1994 edition.3. Loevinger R, Budinger T, Watson, E: MIRD Primer for Absorbed Dose Calculations, Society of Nuclear Medicine, 1991.
Meanwhile, in a general process of the thyroid uptake measurement, the distance from a scintillator of a detector to a thyroid is maintained within a range of about 25 to 30 cm. In a case where an isotope of iodine is used, the measurement is generally carried out after about 18˜24 hours from the administration of the radiopharmaceutical. Additionally, the measurements may be carried out after 2 hours and 6 hours from the administration.
Herein, a neck, thigh (for background measurement), and a neck phantom (before and after administration of dose) are measured. An RAIU (Radioiodine uptake) is calculated using the equation below.
                              R          ⁢                                          ⁢          A          ⁢                                          ⁢          I          ⁢                                          ⁢          U                =                                                            Neckcounts                ⁡                                  (                                      c                    ⁢                                                                                  ⁢                    p                    ⁢                                                                                  ⁢                    m                                    )                                            -                              ThighCounts                ⁢                                                                  ⁢                                  (                                      c                    ⁢                                                                                  ⁢                    p                    ⁢                                                                                  ⁢                    m                                    )                                                                                    Ad                ⁢                                                                  ⁢                                  min                  ·                                      Counts                    ⁡                                          (                                              c                        ⁢                                                                                                  ⁢                        p                        ⁢                                                                                                  ⁢                        m                                            )                                                                                  -                              BackgroundCounts                ⁢                                                                  ⁢                                  (                                      c                    ⁢                                                                                  ⁢                    p                    ⁢                                                                                  ⁢                    m                                    )                                                              ×                      100            ⁢                                                  [            %            ]                                              (        1        )            
In a case where Tc99m Pertechnetate (TcO4−) is used, it is easy to secure a radioisotope, and it is possible to carry out uptake measurement after about 10˜20 minutes from an intravenous injection. Thus, compared to a conventional iodine (123I or 131I) methods, it has following advantages; 1) the radiation exposure of the body can be significantly reduced, 2) the convenience of a patient and a technician is improved, 3) a cost is reduced, and 4) in a case where 99mTc imaging study (image acquisition using 99mTc) is simultaneously carried out to obtain a thyroid image, the convenience is increased.
By the recent general use of 99mTc Pertechnetate (TcO4−) thyroid imaging with a gamma camera, a thyroid uptake measurement using 99mTc Pertechnetate (TcO4−) shows a tendency to be carried out prior to thyroid imaging.
However, when an isotope of 5˜10 mCi is administered to acquire an image, a conventional thyroid uptake measurement apparatus is easily saturated due to its low counting capacity. Thus, a thyroid uptake measurement is generally carried out prior to an image test by injecting a small amount (about 0.5 mCi) of isotope.
Therefore, inconvenience will not be avoidable in that an intravenous injection has to be delivered to a patient twice, i.e., one for thyroid uptake and the other for thyroid imaging. Also, there is a problem in that from the standpoint of a patient management, the throughput is ineffective.
Also, even if a high counting-rate thyroid uptake measurement apparatus exists, the reliability on the measured data collected for thyroid radiation uptake calculation is significantly reduced due to pile-up of radiation signal in consideration of the geometrical structure of a thyroid measurement apparatus and the radiation generation per unit time of 5˜10 mCi of isotope.